1. Field of the Invention
The present invention relates to a sewing machine, in particular for executing assembling seams between two parts of a workpiece, of the type comprising: a base; a horizontal work supporting bed on which the workpiece is laid down; a needle plate arranged to engage the workpiece parts at respectively facing edges; feeding means acting through the needle plate for moving the workpiece forward according to a predetermined stitching direction; a presser foot elastically acting on the workpiece at the needle plate; sewing means acting at the needle plate for making a seam on the workpiece.
The present invention also relates to a sewing method put into practice by said sewing machine.
2. Prior Art
It is known that in sewing machines in general, such as trimming machines, flat bed machines or other sewing machines designed to execute assembling operations, it is normally provided that the parts to be assembled and forming the workpiece be arranged on a horizonal work supporting bed in a mutually superposed position. The junction edges of the parts along which the assembling seam is to be executed, are operatively engaged between a so-called "needle plate", disposed in coplanar relation with the work supporting bed and a presser foot disposed parallelly over the needle plate and elastically urged towards said plate. One or more feed dogs operate through the needle plate under the, presser foot for causing the workpiece to be dragged along according to the direction of the sewing which is simultaneously carried out upon the action of one or more needles reciprocating in a vertical direction through the needle plate itself and cooperating with one or more loopers acting under the needle plate or astride thereof.
Although the above sewing machines give satisfactory results, some problems are encountered when the workpiece parts to be assembled are provided with patterns, such as stripes, checks or the like that must mate in a predetermined manner at the seam joining the parts.
In fact, since the two fabric parts must be necessarily disposed in superposed relation with respect to each other on the work supporting bed and needle plate, at least the pattern of the part disposed underneath is inevitably concealed to the operator's sight.
The only pratical attempt that the operator can A make to solve this problem is to dispose the patterns in a matching relationship when the parts to be assembled are arranged on the work supporting bed. This is however a rather empiric solution in that during the actual execution of the sewing, that is exactly in the most decisive step to the ends of a successful result, there is no possibility of verifying the alignment between the patterns.
In addition, the overlapping of the parts of a workpiece involves great difficulties of practical nature when the workpiece has great surface extensions and/or is very bulky.
There are also assembling machines in which the two parts to be assembled are coplanarly laid down on the work supporting bed, being disposed in side by side relation. The junction edges to be sewn together are moved close to each other and guided on the needle plate which in this case too is located coplanar with the work supporting bed.
During the working step, the junction edges advancing towards the sewing region are moved clone to each other as far as they get in mutual contact and are folded vertically upwardly. At this point the junction edges are trimmed by trimming means associated with the presser foot and are then brought to a position in which they rest on the needle plate before encountering the sewing means.
When sewing machines of the above type are used, however the alignement of the patterns and decorative designs reproduced on the two workpiece parts can be verified in a relatively easy manner only in those case in which the decorative designs are visible on both surfaces of the individual parts. If, on the contrary, the decorative designs are reproduced, for example by printing, only on the face designed to form the exposed surface of the finished product, the operator is almost completely prevented from carrying out said checking. In the connection it is in fact to be pointed out that the fabric parts to be assembled must be disposed on the work supporting bed with the respective decorative designs facing downwardly for enabling the execution of a non-visible seam on the finished product
In addition, the sewing machines of this type too can give rise to some problems when the parts to be assembled are very large and bulky. In particular, the maximum dimensions that the parts of a workpiece can have i s substantially defined by the space located under the arm supporting the head over the needle plate, which head in turn contains the needle driving mechanisms.